Many reasons exist for dispensing liquid adhesives, such as hot melt adhesives, in the form of a thin filament with a controlled pattern. One technology capable of dispensing controlled patterns of thin filaments is known as controlled fiberization (for example, CF® technology from Nordson Corporation). CF® technology is especially useful for accurately covering a wider region of a substrate with adhesive dispensed as single filaments or as multiple side-by-side filaments from nozzle passages having small diameters, such as on the order of 0.010 inch to 0.060 inch.
CF® technology is often used to improve control over adhesive placement. This may be especially useful along the edges of a substrate and on very narrow substrates, for example, such as on strands of material (e.g., LYCRA® by INVISTA) used in the leg bands of diapers.
Conventional swirl nozzles or die tips typically have a central adhesive discharge passage surrounded by a plurality of air passages. The adhesive discharge passage is centrally located on a protrusion that is symmetrical in a full circle or radially about the adhesive discharge passage. A common configuration for the protrusion is conical or frustoconical with the adhesive discharge passage exiting at the apex. The air passages are arranged in a radially symmetric pattern about the central adhesive discharge passage. The air passages are directed in a generally tangential manner relative to the adhesive discharge passage and are all angled in a clockwise or counterclockwise direction around the central adhesive discharge passage.
Conventional meltblown adhesive dispensing apparatus typically comprise a nozzle body having multiple adhesive or liquid discharge passages disposed along an apex of a wedge-shaped member and air passages of any shape disposed along the base of the wedge-shaped member. The wedge-shaped member is not a radially symmetric element. Rather, it is typically elongated in length relative to width. The air is directed from the air discharge passages generally along the side surfaces of the wedge-shaped member toward the apex, and the air impacts the adhesive or other liquid material as it discharges from the liquid discharge passages to draw down and attenuate the filaments. The filaments are discharged in a generally random manner.
Various types of nozzle bodies, such as those of the type described above, have been used to dispense adhesive filaments onto one or more elastic strands. Each strand is typically aligned and directed by a strand passage proximate the corresponding adhesive discharge passage. The strands tend to acquire airborne particulates present in the environment surrounding the liquid adhesive dispensing apparatus. These airborne particulates consist of dust and other contaminants that primarily originate from the processing operations performed by the production line. In addition, the strands, particularly those available from Fulflex, Inc. may be intentionally coated with particulates, such as talc, to facilitate release when extracted from their packaging. In addition, other strand manufactures may add pigments to the strand material to color the strand. Typically, the coloration pigments are abrasive to the nozzle body and, consequently, wear rate on the nozzle may be appreciably higher with colorized strand materials.
Furthermore, as each strand interacts with the corresponding strand passage, the particulates, regardless of origin, may be wiped off and accumulate or agglomerate into larger masses. The agglomerated masses of particulates may dislodge from the strand passage and incorporate into the dispensed adhesive filament. For example, the agglomerated mass may be dislodged by a knot that is formed between the trailing end of a first length of strand material and the leading edge of a second length of strand material joined to provide a continuous strand. Alternatively, the agglomerated mass may remain resident in the guide and increase in dimensions to such an extent that the strand itself is displaced or removed from the guide. In multi-strand dispensing operations, an adjacent guide may capture the displaced strand, which disrupts the application of adhesive to the strands and ultimately produces defective product because the strands are adhesively bonded to a substrate with improper positioning. The reduction in product quality may be significant and may increase the manufacturing cost.
Yet another difficulty associated with dispensing adhesive onto a guided, moving strand arises from contact between the strand and the strand passage. Specifically, the strand wears the metal surfaces of the nozzle body and the metal surfaces of the strand passages due to frictional wear. Eventually, the wear may necessitate replacement of the nozzle body.
What is needed, therefore, is a nozzle body for dispensing a liquid filament onto a substrate in which the difficulties associated with strand guiding are reduced or eliminated.